One in five men become depressed after becoming fathers as they juggle lack of sleep, extra responsibilities and a changed relationship with their partners, new research shows.

By the time their first child is 12, 21% of fathers have had at least one episode of depression, according to an in-depth study funded by the Medical Research Council (MRC).

The findings provide strong evidence that postnatal depression affects significant numbers of men as well as women, and last night prompted calls for fathers-to-be to have their mental state assessed by the NHS in the same way as expectant mothers during their pregnancy. There are worries that problems with a parent's wellbeing can damage their children's behaviour and development.

Research scientists led by Professor Irwin Nazareth, director of the MRC's general practice research framework, studied 86,957 families who received medical care between 1993 and 2007. They identified depression among parents by analysing diagnoses of the condition and antidepressant prescriptions.

Some 3% of fathers had had depression in the first year of their child's life, rising to 10% by the time their offspring was four, 16% by the age of eight and 21% by 12, it was found.

The study also underlined how postnatal depression among mothers is much more common. Of those studied, 13% had been depressed within a year of giving birth, 24% by the time their child reached four, 33% by eight and 39% by the age of 12.

The researchers say the stresses of having a child trigger the depression – such as too little sleep, changed responsibilities and extra pressures being placed on the parents' relationship.

Professor Steve Field, leader of the UK's 44,000 family doctors, said: "This is the best piece of research I've seen on this important but under-appreciated area of medical care. As a GP, I have often seen fathers stressed and depressed, particularly in the first year or two after becoming a parent."

Men who are adapting to the new duty of parenthood while continuing in their job are under stress, and many do not go to see their GP to talk about any fears and worries they may have, added Field, the chairman of the Royal College of GPs.

"This should raise awareness of the stresses and potential problems ahead for dads and dads-to-be and also encourage GPs to screen men, if appropriate. This study should help improve the quality of dads' lives and ensure that talking therapies or other treatments, if needed, are used early."

Rob Williams, chief executive of the Fatherhood Institute, said: "For too long there's been the assumption that it's depression and other mental health problems in mothers that has an impact on children. But in reality, the impact of a father's poor mental health on his children is also powerful.

"The study is likely to have underestimated the numbers of fathers who experience depression, because we know fathers are less likely than mothers to seek help with depression."

Both GPs and health visitors should screen fathers as well as mothers for depression, especially when the woman is depressed, as their partners are more likely to feel the same, Williams added.

"We are missing a golden opportunity to forewarn new parents of the challenges they might face once their baby arrives. Parents need to be told about the risks of depression for both mothers and fathers and they should also be told about the signs which they should be looking out for in their partner."